A subject of the present invention is additives intended to improve the wear resistance and the lubricity of diesel or biodiesel fuels but also their lacquering resistance. The present invention also relates to the use of additive compositions for improving the lacquering resistance of higher-grade (bio)dieselfuels.
In many countries the sulphur content of diesel (B0) or biodiesel (Bx) fuels has been subject to a reduction for environmental reasons, in particular in order to reduce the SO2 emissions. For example in Europe, the maximum sulphur content of road diesel fuels is currently 10 ppm by mass.
As well as reducing the sulphur content, the methods of preparation of low-sulphur diesel fuel bases, for example hydrotreatment methods, also reduce the polycyclic aromatic compounds and polar compounds contained in these fuel bases. It is known that diesel fuels having a low (less than 100 ppm by mass) or very low sulphur content have a reduced ability to lubricate the engine fuel injection system, which results for example in early failure of the engine fuel injection pump during the lifetime of the engine, failure occurring for example in high-pressure fuel injection systems, such as high-pressure rotary distributors, in-line pumps, combined pump-injector units and injectors.
Lubrication and/or anti-wear additives for fuel oils have been described in EP 680506; these additives include a carboxylic acid ester and an alcohol, in which the acid has from 2 to 50 carbon atoms, and the alcohol has one or more atoms; one of the preferred additives is glycerol monooleate (GMO). EP 839174 describes lubricant additives comprising:                a) an ester obtained by reacting an unsaturated monocarboxylic acid and a polyhydroxylated alcohol        b) an ester obtained by reacting an unsaturated monocarboxylic acid and a polyhydroxylated alcohol having at least 3 hydroxy groups,        
the esters a) and b) being different. Apart from their lubricant properties, these mixtures of esters have a particularly good filterability (measured according to standard IP 387); the preferred mixtures of esters are the mixtures mainly comprising glycerol monooleate and glycerol monolinoleate, preferably in substantially equal proportions.
EP 915944 describes anti-wear additives for low-sulphur diesel fuels constituted by a combination of at least one monocarboxylic aliphatic hydrocarbon, saturated or unsaturated, with a linear chain comprised between 12 and 24 carbon atoms and at least one polycyclic hydrocarbon compound chosen from the group constituted by the natural resin acids, and derivatives of carboxylates of amines, esters and nitriles of these acids. These additives can for example be derived from “tall oil”. However, the diesel fuels and in particular the higher-grade fuels to which these anti-wear additives have been added are sometimes found to have unsatisfactory lacquering-resistance properties.
Diesel fuels on the market must meet national or supranational specifications (for example standard EN 590 for diesel fuels in the EU). For commercial fuels, there is no legal obligation regarding the incorporation of additives (chemical compounds incorporated in fuels to improve their properties, for example additives for improving low temperature resistance); the oil companies and the distributors are free to add or not add additives to their fuels. From the commercial standpoint, in the field of distribution of fuels, a distinction is made between the “lowest price fuels”, with little or no additives, and higher-grade fuels, in which one or more additives are incorporated to improve their performance (above the regulation performance). Within the meaning of the present invention, by higher-grade diesel fuel or bio diesel fuel is meant any diesel or biodiesel to which at least 50 ppm by mass of at least one component chosen from deposit reducers, detergents, dispersants has been added. Diesel fuels of the B0 type, which do not contain an oxygen-containing component are distinguished from biodiesel fuels of the Bx type which contain x % (v/v) vegetable oil esters or fatty acids, more usually methyl esters (FAME or VOME).
It has been noted that some higher-grade diesel or biodiesel fuels sometimes cause deposits on the injector needles of injection systems of diesel engines, in particular those of Euro 3 to Euro 6 type. This phenomenon of deposits is also known by the term lacquering, which will be used hereinafter, or the acronym IDID (internal diesel injector deposits). Within the meaning of the present invention, the lacquering phenomenon does not refer to deposits outside of the injection system relating to the coking or fouling of injection nozzles as simulated for example by the standard engine test CEC F098-08 DW10B, especially when the fuel tested is contaminated with metallic zinc.
The lacquering phenomenon can be localized on the end of the injector needles, both on the head and on the body of the needles of the fuel injection system but also throughout the system controlling the needle lift (valves) of the injection system, for vehicle engines operating on diesel or biodiesel fuel, and in particular for higher-grade (bio)diesel fuels. This lacquering phenomenon can eventually generate a loss of flow rate of fuel injected and therefore a loss of engine power.
Generally a distinction is made between 2 types of deposits of the lacquering type:
1. deposits that are rather whitish and powdery; on analysis, it is found that these deposits consist essentially of soaps of sodium (sodium carboxylate, for example) and/or of calcium (type 1 deposits);
2. organic deposits resembling coloured varnishes localized on the needle body (type 2 deposits).
Regarding the type 1 deposits, there are many possible sources of sodium in biodiesel fuels of the Bx type:                catalysts for transesterification of vegetable oils for producing esters of the fatty acid (m)ethyl ester type such as sodium formate;        another possible source of sodium can originate from the corrosion inhibitors used when petroleum products are conveyed in certain pipes, such as sodium nitrite;        finally, accidental exogenous pollution, via water or air for example, can contribute to the introduction of sodium into fuels (sodium being a very wide occurring element).        
There are many possible sources of acids in fuels of the Bx type, for example:                residual acids in biofuels (see standard EN14214 which stipulates a maximum permitted level of acids)        corrosion inhibitors used in the conveyance of petroleum products in certain pipes such as DDSA (dodecenylsuccinic anhydride) or HDSA (hexadecenylsuccinic anhydride) or some of their functional derivatives such as acids.        
With regard to type 2 organic deposits, some publications state that they may in particular result from reactions between deposit reducers/dispersants (for example of the polyisobutylenesuccinimide (PIBSI) type) and acids (which would be present inter alia as impurities of esters of fatty acids in biodiesel). In the publication SAE 880493, Reduced Injection Needle Mobility Caused by Lacquer Deposits from Sunflower Oil, the authors M Ziejewski and H J Goettler describe the lacquering phenomenon and its harmful consequences for the operation of engines operating with sunflower oils as fuel. In the publication SAE 2008-01-0926, Investigation into the Formation and Prevention of Internal Diesel Injector Deposits, the authors J Ullmann, M Geduldig, H Stutzenberger (Robert Bosch GmbH) and R Caprotti, G Balfour (Infineum) also describe the reactions between acids and deposit reducers/dispersants to explain the type 2 deposits.
Furthermore, in the publication SAE International, 2010-01-2242, Internal Injector Deposits in High-Pressure Common Rail Diesel Engines, the authors S. Schwab et al explain that the internal parts of the injectors are generally covered with a slightly coloured deposit that is visible to the naked eye. Their analyses showed that it mainly comprises sodium salts of alkenyl (hexadecenyl or dodecenyl) succinic acids; the sodium originating from dehydrating agents, from caustic solutions used in the refinery, from tank bottom water or from seawater, and the succinic diacids being used as corrosion inhibitors or present in multifunctional additive packages. Once formed, these salts are insoluble in low-sulphur diesel fuels, and as they are in the form of fine particles they pass through diesel filters and are deposited inside the injectors. In this publication, the development of an engine test is described, making it possible to reproduce the deposits. This publication emphasizes that only the diacids generate deposits, in contrast to monocarboxylic acids or the neutral esters of organic acids.
In the publication SAE International, 2010-01-2250, Deposit Control in Modern Diesel Fuel Injection System, the authors, R. Caprotti, N. Bhatti and G. Balfour, also investigate the same type of internal deposits in the injectors and assert that the appearance of deposits is not linked specifically to one type of fuel (B0 or containing FAME(Bx)) nor to vehicles of one type (light vehicles or heavy goods vehicles) equipped with modern types of engines (common rail). They demonstrate the performance of a new deposit reducer/dispersant, effective on all types of deposits (coking and lacquering).
The document DE 10 2004 055589 describes esters obtained from carboxylic acids comprising from 11 to 21 carbon atoms and diglycerol, oligoglycerols and/or polyglycerols. These esters are used for improving the lubricity of diesel fuel. This document does not relate to improving the lacquering resistance of fuels of higher-grade (bio)diesel type.
The deposits due to the lacquering phenomenon are insoluble in low-sulphur diesel fuels and in biodiesel fuels. These deposits are in the form of fine particles and can pass through diesel filters and can then be deposited inside the injectors. The accumulation of deposits of the lacquering type as described above can lead to the following problems:                a slowing of the response of the fuel injector,        sticking of internal components, which can lead to a loss of control of injection time as well as of the amount of fuel supplied per injection,        a loss of manoeuvrability of the vehicle,        variations in power,        an increase in fuel consumption,        an increase in pollutants,        a disturbance in combustion, since the amount of fuel injected will not be that envisaged theoretically and the injection profile will be different,        an unstable idle of the vehicle,        an increase in engine noise,        a lowering of the quality of combustion over the long term,        a lowering of the quality of atomization.If there is a heavy deposit of the lacquering type, the vehicle could have great difficulty starting, or even not start at all, since the needle permitting injection would be blocked.        
The present invention makes it possible to overcome the problems indicated above. The present invention proposes additives capable of really improving not only the wear resistance of (bio)diesel fuels having a low sulphur content, typically less than 100 ppm by mass, but also the lacquering resistance of higher-grade (bio)diesel fuels, i.e. containing as additives at least 50 ppm by mass of at least one component chosen from deposit reducers, detergents, dispersants.